It is known in the art to use pre-treatment of print media (e.g., paper) in aqueous ink jet printing in order to improve print quality, in particular, on machine coated print media. Known pre-treatment compositions comprise water and an aggregation agent for destabilizing and pinning pigment particles and/or for destabilizing of dispersed polymer particles (e.g. latex) in order to facilitate film formation. Examples of aggregation agents are also known in the art and comprise, but are not limited to, acidic compounds, (polyvalent) metal compounds and oligomeric organic polycations.
Aqueous inks comprising alkali soluble latices are also known in the art. Alkali soluble latices are in a dispersed state at low pH (acidic) and may be added to ink compositions in that state. When the pH of the inks is adjusted to a higher pH (alkaline), the alkali soluble latex resin dissolves (at least partly) in the ink composition as to form a polymer thickening agent in the ink, while maintaining or improving the jettability of the ink composition.
It is however a disadvantage of such ink compositions that once printed and dried, the prints are water sensitive (i.e., have an inferior water fastness) due to the solubility of the alkali soluble latex resin when reintroducing water to the printed surface.
When a known acidic pre-treatment composition is used in combination with an ink composition comprising an alkali soluble latex resin the above disadvantage can be overcome or at least mitigated. However, in order to achieve an acceptable water fastness, acidic pre-treatment compositions with very low pH may be required. A disadvantage of such low pH pre-treatment compositions is that they are corrosive towards materials used in printers and in particular in printheads. Thus, printer parts including printheads made of such materials may be affected or even permanently damaged when such printer parts come into contact with such strong (low pH) acidic pre-treatment compositions.
It is therefore an object of the present invention to provide a pre-treatment composition for improving the water fastness of printed matter made with aqueous ink compositions comprising alkali soluble latex resins that is non-corrosive with respect to used materials in the printer and without imparting the print quality.